This project is focused on the role of transposons in the process of spontaneous mutation and chromosome rearrangement in Drosophila. With Prof. Lim we are studying a strain that showed a burst of activity by the retrotransposon gypsy, exhibiting amplified copy number and high mobility. This caused a high rate of spontaneous X chromosome mutation due to insertion/excision events. The mobilization is shown to occur very early after fertilization, causing somatic and germline mosaicism for mutations. We are studying the conditions that activate gypsy and also how an active strain becomes stable. Transposons are also known to mediate gross chromosomal rearrangements through a process of asymmetrical pairing and exchange. This process occurs both as intrachromosomal and interchromosomal exchanges to produce, in the former case, deletions or inversions depending on the relative orientations of the transposons and in the latter case. duplications and deficiencies and possibly translocations. We are studying a large collection of such rearrangements and characterizing the breakpoints at the molecular level to establish the role of the transposons and investigate the mechanism of exchange.